This invention relates to semiconductor force transducers, and more particularly to an improved packaging means for a transducer employing a folded leaf spring membrane.
In U.S. Pat. No. 4,050,049 issued Sept. 20, 1977, to Albert P. Youmans and assigned to the same assignee of this invention, there is disclosed a force transducer which employs a semiconductor chip having a thin membrane formed in the shape of a folded cantilever spring. The semiconductor spring membrane incorporates four piezoresistive elements formed by ion implants or diffusions at high stress regions of the spring membrane. Two of the piezoresistive elements are oriented so that their resistance increases with acceleration and the other two are oriented so that their resistance decreases with acceleration. The piezoresistive elements are connected in a bridge configuration so thay any acceleration unbalances the bridge and produces a signal that is directly proportional to the acceleration force.
Several requirements must be met by the packaged transducer to make it function properly. It must be thermally isolated from the environment so that the transducer will be insensitive to external changes in temperature. For operation as an accelerometer, the spring membrane must be critically damped so as not to produce a signal after the accelerating force has terminated. Lastly, the transducer must be protected from corrosive or electrically conductive environments.